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This invention relates to ink jet printers, and more particularly to a mount for accurately positioning an ink jet printhead in a desired position for imprinting information or indicia on a surface of a series of articles (e.g. boxes or packages) conveyed past the printhead. The mount of this invention maintains a predetermined spaced relationship between a printing face of the printhead and the surface of the article or substrate to be imprinted.
In conventional ink jet print apparatus used, for example, for imprinting packages or boxes conveyed along a packaging line, each printhead typically has an array of orifice nozzles or ink outlet openings from which ink is expelled in the form of droplets. The droplets are expelled in a predetermined pattern toward a side of the carton or object (or other surface) to be imprinted such that upon the ink striking the carton surface, a predetermined indicia is imprinted on the surface. For example, such ink jet printing apparatus may be used to print a variety of information (indicia) on a carton or package, such as trademarks, lot numbers, serial numbers, production dates, shipping date information, bar codes, graphics, and other pertinent information. The ink nozzles or outlets of the printhead are in communication with a supply of ink. A programmable controller regulates the operation of the valves or other well known means for forming and expelling the ink droplets so as to cause the ink to be emitted from the nozzles according to a preselected pattern so as to imprint the desired information or indicia on the surface to be imprinted.
Generally, the ink nozzles or outlets are located on a print face of the printhead with this print face being spaced a short distance (referred to as the orifice-to-substrate distance or the standoff distance) from the surface to be imprinted. Thus, ink emitted from the ink jet nozzles must travel from the printface to the surface to be imprinted across the orifice-to-substrate distance (which is typically a small fraction of an inch) to form the ink droplets of the desired shape and size and to form an ink droplet pattern of the desired resolution so as to form the indicia to be imprinted. Typically, an ink droplet grows wider as it travels from the outlet opening or nozzle to the surface to be imprinted. As the width (diameter) of the droplet increases, a larger or irregular dot will be printed upon the surface impacted by the droplet. As the droplet gets wider, the outer edges of the printed dots loose precision or resolution, and the quality of the printing deteriorates. Likewise, if the spacing of the printhead is too close to the surface to be imprinted, the droplets may not sufficiently overlap and thus the quality of the indicia to be imprinted will be adversely affected. Accordingly, the orifice-to-substrate distance of the printhead is a critical parameter in maintaining the quality of the indicia to be imprinted.
Reference may be made to U.S. Pat. No. 4,378,564 for a disclosure of a typical ink jet printing system for imprinting packages in a packaging line.
In a typical packaging line, the surfaces of cartons or other articles to be imprinted move along a conveyor path past one or more ink jet printheads. For example, the surfaces to be printed are typically the side of a carton or package being conveyed along a conveyor belt past an ink jet printing station. Of course, there are typically a series of packages one after the other that are conveyed past the print station. It is common to have one or more printheads on opposite sides of the conveyor path so that the printing can be done on opposite faces of the packages.
To guide the packages into position relative to the printhead or printheads, guide rails are commonly provided along the conveyor so as to orient and position the package on the conveyor line so that the surfaces of the packages are positioned in predetermined planes relative to the line of movement of the conveyor and relative to the print station as they move therepast. The guide rails confine the packages between them as they are transported by the conveyor.
Packages in such a packaging line are typically of the same nominal size, but they may vary in width, height, and length due to manufacturing tolerances. In addition, there may be irregularities or undulations (bulges) in the faces of the packages to be printed. Therefore, the span between the guide rails must be great enough to accommodate the widest of the packages as permitted by a range of package tolerances. Smaller packages within this permitted range of tolerances may not contact the rails. Accordingly, although the guide rails position the packages at nominal distances from the printhead, those distances vary as the packages to be imprinted are conveyed past the printheads. Further, it is generally a desire of such conveyor lines that the widest range of package tolerance possible be accommodated by the printheads. In order to achieve optimal printing quality and resolution, it is necessary that the ink jet printhead be mounted to move toward or away from the conveyor line such that the printing head may be positioned to have the optimal orifice-to-substrate distance from the surface to be imprinted, regardless of size variations of the packages to be printed and regardless of surface undulations or irregularities of the package.
Means have been developed for reducing the orifice-to-substrate distances of printheads and for maintaining a tighter tolerance of the orifice-to-substrate distances so as to enhance print quality and resolution. One such means is shown in co-assigned U.S. Pat. No. 4,814,795, which is herein incorporated by reference. In this last-mentioned patent, printheads of such ink jet printing apparatus are spring biased toward the surface to be printed so as to accommodate a range of package sizes conveyed past the printhead and so as to maintain a substantially constant orifice-to-substrate distance between the ink jet nozzles and the surface of the package to be printed. While this prior art printhead mount worked well for its intended purpose, this printhead mount required an additional separate slide mount to support the printhead. The slide mount included horizontal rods on which slide bearings were mounted which in turn carried the printhead for transverse movement of the printhead toward and away from the surface of the package to be imprinted as the package was conveyed past the printhead. The perpendicular travel of the mount relative to the conveyor caused the slide rods to be subject to being bent or peened in the operative life of the slide mount. Of course, an imperfection in one of the slide rods would impede the proper operation of the slide and would have a negative effect on print quality. Further, as the speed of the packages conveyed past the printhead was increased, the engagement of the printhead by packages at such higher speeds resulted in sudden impact loads being applied to the printhead and/or the mount which resulted in bouncing of the printhead and the mount. In turn, these impact forces and the consequent bouncing of the printhead resulted in poorer quality printing and resolution, as compared to printing at slower speeds. In addition, the impact loads, under certain conditions, could cause the printhead to de-prime (i.e.., lose its ink supply) such that is would not properly print.
U.S. Pat. No. 5,101,224, which is also assigned to the same assignee as the present invention and which is also incorporated herein by reference, solved some of the aforementioned problems. Specifically, this last noted prior art patent provided an ink jet printhead support that carried the printhead on a pivotally mounted support that was biased inwardly toward the surface of a package or article by means of a torsion spring. The support permitted vertical and horizontal positioning of the printhead, and eliminated the above noted slide rods, however, this printhead support was complex in construction and the action tended to skew the print, depending on the placement of the package relative to the pivot point. In addition, this prior art printhead support was not sufficient for higher resolution printheads.
Among the several objects and features of the present invention will be noted the provision of a support or mount for an ink jet printhead which maintains an optimal orifice-to-substrate distance between the printing face of the printhead and a surface to be printed conveyed past the printhead;
The provision of such a printhead mount that smoothly absorbs such impact energy and which assures fast, but smooth movement of the printhead as the latter moves toward and away from the package surface to be imprinted, and thus prevents de-priming of the printhead;
The provision of such a printhead mount that effectively absorbs impact energy of a package being conveyed past the printhead at relatively high speed engaging the printhead mount;
The provision of such a printhead mount that smoothly absorbs such impact energy and which assures fast, but smooth movement of the printhead as the latter moves toward and away from the package surface to be imprinted, and thus presents de-priming of the printhead;
The provision of such a printhead mount which assures a tighter range of orifice-to-substrate distance tolerances and which maintains such tolerances as the packages are conveyed past the printhead so as to maintain high resolution print quality;
The provision of such a printhead mount which allows the printhead to be positioned in a park position in which the largest package within a range of package sizes clears the printhead as the package is conveyed therepast;
The provision of such a printhead mount which allows the printhead to be positioned in an extended print position in which the printhead mount is engaged by any package within this range of package sizes conveyed past the printhead and which positions the print face of the printhead relative to the surface of the object or package to be imprinted with a desire standoff distance (i.e., orifice-to-substrate distance) so as to enable the imprinting of high resolution indicia on the object;
The provision of such a printhead mount which permits movement of the printhead toward and away from the package surface to be imprinted with the movement of the printhead being taken up by a resilient slide or other mechanism which is operable in an angled or oblique range of directions so as to lessen impact load upon the printhead as the latter is engaged by a package conveyed along said conveyor path and as the printhead is forced from its extended position to its desired printing position; and
The provision of such a printhead mount which is of rugged and economical construction, which has a wide range of operational tolerances, and which is reliable in operation and has a long service life.
Briefly stated, a mount of the present invention mounts an ink jet printhead in position to imprint indicia on a surface of an object conveyed along a path past the printhead. The mount comprises a support and a slide carried by the support. The slide has a slide body connected to the support, a slide member movable relative to the slide body along a slide axis between an extended position and a retracted position, and means for resiliently biasing the slide member relative to the slide body toward its extended position. Means is provided for carrying the slide relative to the support such that the slide axis may be adjusted relative to the support so as to position the slide axis within a range of slide angles relative to the direction of movement of the object conveyed along the path or to be angled toward the object approaching the printhead. The printhead is carried by the slide member and is engageable by the object conveyed along the path such that the printhead is forced to move from its extended position toward its retracted position with the slide moving along its slide axis against the bias of the resilient biasing means thereby to resiliently maintain the printhead in printing relation with the surface of the object as the latter is conveyed past the printhead.
Alternatively, a mount of the present invention mounts an ink jet printhead in position to imprint indicia on the surface of an object conveyed past the printhead includes a support. A slide is carried by the support with the slide comprising a slide body connected to the support, and a slide member movable along a slide axis relative to the slide body between an extended position and a retracted position. The slide includes means for resiliently biasing the slide member relative to the slide body toward its extended position. The slide is oriented on the support such that the slide axis angles toward an approaching object to be imprinted at an oblique angle with respect to the path of the object. The printhead is carried by the slide member and is engageable by the object conveyed along the path such that the printhead is forced outwardly away from the object in such manner that the slide is forced to move from its extended position towards its retracted position along the slide axis at the above noted oblique angle. The forced movement against the bias of the resilient biasing means thereby lessens the impact of the printhead being engaged by the object as the latter moves into engagement with the printhead and to resiliently maintain the printhead in printing relation with the surface of the object as the latter is conveyed past the printhead.
Other objects of this invention will be in part apparent and in part pointed out hereinafter.